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Abstract:

There is provided a splitter circuit means for use with a CATV network
comprising a signal input (34) in communication with a transformer or
balun (32) to supply two signal outputs (36, 38), with a resistor (52)
connected in parallel between the outputs (36, 38) and wherein additional
capacitive, inductive and resistive elements (48, 50, 52, 54) are
associated with the resistor (42), thereby to give an insertion loss in
to out in the range of 3 to 10 dB and isolation 10 out to out of <17
dB for signal frequencies in the range 1125 MHz to 1700 MHz, while at the
same time maintaining good RF performance in the frequency range 5 MHz to
1000 MHz.

Claims:

1. A splitter circuit for use with a CATV network comprising a signal
input in communication with a transformer or balun to supply two signal
outputs, with a first resistor connected in parallel between the outputs
and wherein a filter unit comprising a single inductive element,
capacitive and resistive elements is associated with the first resistor,
thereby to give an insertion loss in to out in the range of 3 to 10 dB,
for signal frequencies in the range 1125 MHz to 1700 MHz.

2. A splitter circuit according to claim 1, wherein the filter unit is
connected in series with the first resistor.

3. A splitter circuit according to claim 1, wherein two capacitive
elements, a second resistor and an inductive element are connected in
parallel with the first resistor.

4. A splitter circuit according to claim 2, wherein the two capacitive
elements are in series with each other and in parallel with the second
resistor and inductive element.

5. A splitter circuit according to claim 3, wherein the single inductive
element has an inductance in the range 10 to 20 nH.

6. A splitter circuit according to claim 3, wherein the first capacitive
element has a capacitance in the range 2 pF to 5 pF with the second
capacitive element having a capacitance in the range 0.1 pF to 3 pF.

7. A splitter circuit according to claim 3, wherein the second resistor
has a resistance in the range 100 to 50 Ohm.

8. A splitter circuit according to claim 1, wherein the splitter circuit
has an insertion loss in to out in the range 3 to 6 dB for signal
frequencies in the range 5 MHz to 1000 MHz.

9. A splitter circuit according to claim 1, having an isolation out to
out of <17 dB for frequencies in the range 1125 MHz to 1700 MHz.

10. A signal splitter incorporating at least one splitter circuit
according to claim 1.

11. A cable television network incorporating one or more splitter circuit
according to claim 1.

Description:

FIELD OF THE INVENTION

[0001] This invention relates to a signal splitter for use in MoCA/CATV
networks, the associated circuitry and a cable television network
incorporating such signal splitters.

BACKGROUND TO THE INVENTION

[0002] A signal splitter, also known as a power splitter, for use in
networks where CATV (cable television) transmission is combined with MoCA
(Multimedia over Coax Alliance) transmission should have good return
loss, low insertion loss and high isolation in the CATV frequency range
(typically 5 MHz to 1000 MHz) to give excellent RF performance.

[0003] However for the MoCA frequency range which in the future is
expected to range from is typically 1125 MHz to 1700 MHz, the signal
splitter should ideally have a low isolation as well as a low insertion
loss so as to reduce transmission loss and thus improve or, in some
cases, enable MoCA transmission between output ports of a plurality of
splitters within an in-home network.

[0004] Most homes have an in-home coaxial network installed to distribute
TV signals to various locations. This network can also be used to
distribute data or other signals to and from these locations.

[0005] With the increasing use of IP (Internet Protocol) and the internet,
in-home networking is becoming very important and whilst there may be an
access point in the home, it can be difficult to distribute data from
this access point to and from various locations in the home. There are
several technologies available to achieve this, for example PowerLine,
MoCA, wireless, fibre optic, and CAT-5. These technologies all have their
weaknesses.

[0006] The advantages of using the existing in-home coaxial networks are
obvious: no new wires are needed and the coaxial cable is a medium with
large bandwidth and very good screening. It is therefore a safe and fast
medium and since it is already in place, it is also an economical
solution.

[0007] However the signal dividers used in existing coaxial networks have
a high isolation between output ports making two-way MoCA communication
very difficult and in many cases even impossible.

[0008] It is an aim of the present invention to provide a signal splitter
and associated circuit means to combine suitable RF performance in the
CATV frequency range with low isolation in the MoCA frequency range.

SUMMARY OF THE INVENTION

[0009] In accordance with one aspect of the present invention, there is
provided a splitter circuit means for use with a CATV network comprising
a signal input in is communication with a transformer or balun to supply
two signal outputs, with a first resistor connected in parallel between
the outputs and wherein a filter unit comprising a single inductive
element, capacitive and resistive elements is associated with the first
resistor, thereby to give an insertion loss in to out in the range of 3
to 10 dB, and preferably an isolation out to out of <17 dB, for signal
frequencies in the range 1125 MHz to 1700 MHz. The frequency band of 1125
to 1700 MHz is the preferred MoCA bandwidth and a splitter circuit with a
low insertion loss over this frequency range improves MoCA transmission
between output ports of associated splitter circuits.

[0010] Preferably the filter unit is connected in series with the first
resistor thereby to prevent signals flowing through the first resistor
for signal frequencies in the range 1125 MHz to 1700 MHz.

[0011] Preferably two capacitive elements, a second resistor and an
inductive element are connected in parallel with the first resistor.
Preferably the two capacitive elements are in series with each other and
in parallel with the second resistor and inductive element. A signal
splitter incorporating such a circuit will have low isolation, low
insertion loss and moderate return loss for signals within the MoCA
frequency range.

[0012] Desirably the inductive element has an inductance in the range 10
nH to 20 nH, more preferably 3 nH to 11 nH.

[0013] The first capacitive element may have a capacitance in the range 2
pF to 5 pF, more preferably in the range 1 pF to 2.5 pF, with the second
capacitive element preferably having a capacitance in the range 0.1 pF to
3 pF, more preferably 1 pF to 1.5 pF.

[0014] The second resistor may have a resistance in the range 100 to 50
Ohm, more preferably 90 to 75 Ohm, where the first resistor has a value
in the range 150 to 50 Ohm, more preferably 110 to 70 Ohm. Typically the
narrower range of values applies where the splitter circuit means is
incorporated into a two-way splitter, the broader range applying for
four-way splitters.

[0015] The splitter circuit means preferably has an insertion loss in to
out in the range 3 to 6 dB for frequencies in the range 5 to 1000 MHz and
an insertion loss in to out of 3 to 10 dB for frequencies in the range
1125 MHz to 1700 MHz. The splitter circuit means preferably has an
isolation port to port of >20 dB for frequencies in the range 5 to
1000 MHz and <17 dB in the frequency range 1125 to 1700 MHz. The
splitter circuit means thus is able to have suitable RF performance in
the CATV frequency range while at the same time having low insertion
loss, low isolation and moderate return loss for signals in the MoCA
frequency range.

[0016] The invention also lies in a signal splitter incorporating at least
one splitter circuit means as aforesaid, so giving two output ports which
are typically associated with subscriber equipment. In such a signal
splitter, the single inductive element may have an inductance in the
range 10 nH to 20 nH, the first capacitive element may have a capacitance
in the range 2 pF to 5 pF and the second capacitive element may have a
capacitance in the range 0.1 pF to 3 pF, with the second resistor
preferably having a resistance in the range 100 to 50 Ohm.

[0017] The signal splitter may incorporate a plurality of splitter circuit
means as aforesaid so as to provide additional output ports. Typically
one splitter circuit means in accordance with the invention will be
connected to two splitters to provide a four-way splitter in accordance
with the invention.

[0018] For signal splitters in which splitter circuits are combined to
give 4, 6, 8, 10 or more ports, the values for the inductive, capacitive
and resistive elements will need to be selected to ensure the desired
insertion loss in to out of between 3 to 10 dB and an isolation out to
out of <17 dB is achieved in the MoCA frequency range.

[0019] In accordance with another aspect of the present invention, there
is also provided a cable television network incorporating one or more
splitter circuit means or signal splitters as aforesaid.

[0020] The invention will now be described, by way of example, with
reference to the accompanying drawings in which:

[0021]FIG. 1 shows a schematic diagram of an in-home CATV and MoCA
network;

[0025] Within the home of a subscriber are a number of devices 12, such as
televisions which receive a signal from a CATV network 14 and are capable
of returning modified signals to the network through set-top boxes 16
which are connected via splitters to a modem 18 which receives and
transmits signals to and from the CATV network 14. Within the home, there
is typically more than one device receiving the signal from the

[0026] CATV network and to supply a signal to each item of subscriber
equipment, a four-way splitter 20 splits the incoming signal to feed a
variety of devices, with if required signals from the four-way splitter
being split again, for example by two-way splitter 22. These splitters
act to combine the signals returned from the consumer's devices.

[0027] The signal or power splitter used in this type of combined
CATV/MoCA network should have the normal specification for the CATV
frequency range as these channels pass through the modem 18 (from IN to
OUT) and are transmitted throughout the in-home network 10.

[0028] For transmission in the MoCA frequency range to be achieved, it is
necessary to have a lower isolation between the output ports of the power
splitters 20, 22 as this will lower the transmission loss. For example:
suppose set-top box 16 transmits to set-top box 16'''. The MoCA
transmission loss will be:

[0034] Since the frequency of MoCA is high, the cable losses are
significant but cannot be avoided. These high cable losses pose yet
another problem: the return loss in the MoCA frequency range at the input
of the two-way splitter will be on average:

[0036] This will increase the isolation between outputs of the two-way
splitter 22 and as such increase transmission loss between certain points
in the network 10.

[0037] A typical prior art two-way signal divider 30 will have a topology
as shown in FIG. 2. This splitter comprises a transformer in the form of
a (typical) 2×2 winding 180 degree balun (balanced to unbalance to
converter) 32, also known in the art as a `fork`, which splits the signal
from an input 34 to provide separate signals to two customer outputs 36,
38. The impedance at the centrepoint of the balun 32 is half of the input
impedance 75 Ohm and the impedances of the outputs 36, 38, each again 75
Ohm, and in the case of a cable TV splitter is 37.5 Ohm. A resistor 42 is
connected in parallel with the balun 32 and typically has a value of 150
Ohm. Frequency response compensation of the circuit is achieved by means
of capacitor 44 which typically has a capacitance of around 2 pF. A
step-up transformer 40 split at (typically) 2 windings and 5 windings is
placed in series between the input 34 and the balun 32, transferring the
37.5 Ohm impedance (at the centre tap of balun 32) to 75 Ohm at the
input.

[0038] This kind of divider has good return loss on all ports and high
isolation between output ports. This is not suitable for in-home signal
transmission when CATV transmission is combined with MoCA transmission in
the frequency range up to 1700 MHz as if the transmission loss of MoCA in
the in-home network is to be lowered for the MoCA frequency range the
following is required:

[0039] low isolation between output ports

[0040]
low insertion loss from in to out

[0041] with a moderate return loss
being acceptable.

[0042] A standard four-way power splitter is created from three standard
two-way splitters as basic building blocks, as is known in the art.

[0043]FIG. 3 shows a power splitter configuration in accordance with the
present invention that does not have the disadvantages of the prior art
power splitter shown in FIG. 2 when used in an in-home coaxial network in
which CATV transmission and MoCA transmission are combined. In the signal
splitter 46 shown in FIG. 3, capacitors 48, 50, resistive element, namely
resistor 52, and inductor 54 are added to the resistor feedback circuit
in the topology shown.

[0044] The resistor 52 is connected in series with inductor 54 and these
two elements are in turn in parallel with series capacitors 48 and 50,
with a connection between the joining points of capacitors 48, 50 and the
joining points of resistor 52 and inductor 54. The filter unit made from
the capacitors 48, 50, resistor 52 and inductor 54 is in turn connected
to resistor 42, such that resistor 42 is in series with the filter unit.
The filter unit prevents signals flowing through the isolating resistor
42 over the frequency range 1125 MHz to 1700 MHz and by blocking this
signal path, the isolation of the splitter is greatly reduced.

[0045] The feedback circuit 58 acts as a filter with no or little
influence at the CATV frequency range from 5 MHz to 1000 MHz but with low
insertion loss in the MoCA frequency range from 1125 MHz up to, or even
beyond, 1700 MHz. This will lower the isolation in the MoCA frequency
range while, at the same time, maintaining low insertion loss, moderate
return loss and excellent RF performance in the CATV frequency range 5
MHz to 1000 MHz. Typically for frequencies in the range 1125 MHz to 1700
MHz, the circuit/splitter has an insertion loss in to out in the range 3
to 10 dB, and isolation out to out of <17 dB.

[0046] Typical values for the components are:

[0047] Resistor 42: 150 to 50 Ohm, more preferably 100 Ohm

[0048] Resistor 52: 100 to 50 Ohm, more preferably 82 Ohm

[0049] Capacitor 44: depending on the ferrite used and the windings, but
typically 1.5 pF to 2.2 pF

[0053] This circuit is a simple implementation and so can be manufactured
using shorter PCB tracks and less PCB surface than more complicated
circuits. Using shorter tracks, avoids performance being degraded at
higher frequencies such as 1700 MHz. Also, because there is only a single
inductor, physical alignment of the value of inductors by bending
inductor windings to be more open or closed is easier than if two
inductors were used.

[0054] The splitter described can be used to make a four-way power
splitter or any other multiple splitter from two-way splitters as basic
building blocks. The feedback circuit 58 can be used as the basic
difference with a standard multiple output CATV splitter.

[0055] When using the splitter of FIG. 3, the transmission characteristics
in the CATV frequency range are substantially not affected while, at the
same time, the transmission loss in the MoCA frequency range improves.
This is also true when more power splitters are cascaded as in a larger
network or when two-way power splitters are used as basic building blocks
in a four-way splitter.

[0056] This power splitter has excellent RF performance in the CATV
frequency range while at the same time having low isolation, low
insertion loss and moderate return loss for the MoCA frequency range up
to 1700 MHz.